For most operations, it is easier to operate on a single cache.
It is usually clear whether operations should quit when finding the first
match, or to operate on all workers. (For example, remove(mondrian.spi.SegmentHeader) tries
to remove the segment header from all workers, and returns whether it
was removed from any of them.) This class just does what seems
most typical. If you want another behavior for a particular operation,
operate on the workers directly.